Aggregation-regulated room-temperature phosphorescence materials with multi-mode emission, adjustable excitation-dependence and visible-light excitation

Constructing room-temperature phosphorescent materials with multiple emission and special excitation modes is fascinating and challenging for practical applications. Herein, we demonstrate a facile and general strategy to obtain ecofriendly ultralong phosphorescent materials with multi-mode emission, adjustable excitation-dependence, and visible-light excitation using a single organic component, cellulose trimellitate. Based on the regulation of the aggregation state of anionic cellulose trimellitates, such as CBtCOONa, three types of phosphorescent materials with different emission modes are fabricated, including blue, green and color-tunable phosphorescent materials with a strong excitation-dependence. The separated molecularly-dispersed CBtCOONa exhibits blue phosphorescence while the aggregated CBtCOONa emits green phosphorescence; and the CBtCOONa with a coexistence state of single molecular chains and aggregates exhibits color-tunable phosphorescence depending on the excitation wavelength. Moreover, aggregated cellulose trimellitates demonstrate unique visible-light excitation phosphorescence, which emits green or yellow phosphorescence after turning off the visible light. The aggregation-regulated phenomenon provides a simple principle for designing the proof-of-concept and on-demand phosphorescent materials by using a single organic component. Owing to their excellent processability and environmental friendliness, the aforementioned cellulose-based phosphorescent materials are demonstrated as advanced phosphorescence inks to prepare various disposable complex anticounterfeiting patterns and information codes.

1)The authors mentioned that the degree of substitution (DS) of CBtCOOH was 0.54. However, the synthetic method indicated that they used different molars of trimellitic anhydride (9.48-14.22 g, 49.38-74.07 mmol). Hence, did the author optimize the reaction to obtain the DS? Whether the products with different molar ratios of trimellitic anhydride could show different RTP performance?
2)The molecularly separated CBtCOONa and the coexistent state of CBtCOONa were fabricated by immobilizing in CaCO3. And the authors also mentioned that the RTP origin is the sodium trimellitate. So, I am curious about the role of cellulose in this system. Is it possible to obtain similar RTP materials using the same method in sodium trimellitate solutions instead of cellulose trimellitate? 3)In the abstract, the authors claimed the method proposed in this work is a general strategy to obtain eco-friendly ultralong RTP materials. However, its universality has not been demonstrated. To check the universality, the author may consider using other RTP units to replace trimellitic anhydride. 4)For Fig. 2, the QYs for all these samples are smaller than 4%, which is a much lower value than other reported RTP systems. The authors may add some comments to it. 5)In a highly dilute solution (0.2 mg/mL), CBtCOONa should exhibit a molecularly dispersed state without aggregation, as shown in Fig. 3a. Usually, no DLS signal can be detected for the dispersed solution. Why are there 2 nm aggregates in this dilute solution? 6)On page 7, the description that "dilute CBtCOONa solutions emitted blue phosphorescence without excitation dependence at 254-310 nm excitation" is misleading. From Fig. S4 and 1b, actually, dilute CBtCOONa solution showed different emission maximum and even green RTP under excitation 365 nm, indicating its excitation-dependent property. 7)For dilute solution and concentrated solution, and metal participated solution of CBtCOONa, the aggregate state and inter/intrachain interactions are totally different. Why did they show almost the same lifetimes of RTP, around 450-498 ns? 8)Calcium carbonate is insoluble in water. How did the author prepare waterborne inks based on CBtCOONa/CaCO3 with different ratios of CBtCOONa? 9)For Fig. 5a, this diagram is oversimplified and doesn't show how to fabricate patterns with those inks. Besides, the detailed methods to fabricate these patterns should be described in the Method. 10)For Fig. 4 and 5, What kind of lamp is used as the visible-light source? What is the wavelength? 11)The authors should polish the manuscript carefully, as several grammatical and spelling mistakes are observed. The logic of the manuscript needs to be improved.
Reviewer #2 (Remarks to the Author): Organic materials with bright and tunable room temperature phosphorescence (RTP) are important for optoelectronic and biomedical applications. Particularly, those from natural sources are even promising considering its biocompatibility, environment-friendliness, and rich sources. In this contribution, by conjugating anionic phenylcarboxylate substituents onto the cellulose chain and further neutralization, the authors constructed the sodium cellulose trimellitate (CBtCOONa) as a kind of RTP material, which demonstrates blue, green, and color-tunable RTP in molecularly-dispersed state, aggregate state, and the coexistence state of the above two, respectively. Noticeably, visible-light excitation was observed from such RTP material as well as other cellulose trimellitates with different metal cations (CBtCOOM). Corresponding characterizations also show the potential of CBtCOONa in advanced anti-counterfeiting inks. Overall, the experimental design and application demo are commendable, and the findings are interesting and important for further exploration of novel RTP materials. Therefore, this reviewer recommends it for publication in Nat. Commun. with some minor revisions. 1. The synthesis of CBtCOOH is proved by 1H NMR and FTIR in the manuscript. However, these characterizations can only verify the coexistence of the cellulose chain and the small molecule in the system, while whether these two parts are conjugated is not sufficiently proved. 2. Line163-164, it is claimed that there is no excitation dependence at 254-310 nm excitation when CBtCOONa content is 4%-20%, which seems not accurate. The main peak is slightly red-shifted as the excitation wavelength changes from 254 to 310 nm in Figure S4(a). 3. Line 222, "phosphor" might be "phosphorescence". 4. Line 255, it is claimed that inter-system crossing is promoted. Are there any further evidences for it? 5. Line 303-304, the red-shifted phosphorescence of CBtCOOIn and CBtCOOLa is attributed to larger radii of In3+ and La3+ and further formed larger aggregates with CBtCOO-chains. Further explanation on this deduction is encouraged. 6. The author discussed multi-color and stimuli-responsive RTP materials in the Introduction part. Some highly related work can be included: DOI: 10.1039/d0cs01087a. Reviewer #3 (Remarks to the Author): In this manuscript, the authors reported a new kind of RTP materials with multi-mode emission, adjustable excitation-dependence and visible-light excitation based on cellulose derivatives.
Experimental results showed that the aggregation regulation of the phosphor groups in cellulose should be mainly responsible for these unique characteristics. The results are interesting and can be published after revisions. 1. In this work, the covalent linkage between anionic phenylcarboxylate and cellulose should be important for the efficient RTP effect. To further certify it, the RTP properties of anionic phenylcarboxylate derivatives and cellulose mixtures through physical doping should be measured to make a careful comparison. 2. How about the molecular weights of cellulose and cellulose trimellitate? The measurements of them would be much helpful to calculate the degree of substitution (DS) of CBtCOOH. 3. The poor solubility of cellulose in common solvents has largely limited its practical applications. In this work, the combination of anionic phenylcarboxylate and cellulose led to the relatively good solubility in aqueous solution, which could largely promote the processibility. Thus, the authors are suggested to add some discussions about it. 4. In Figure 1 and 4, the afterglow times of aggregates are always longer than those of single molecular chains. This is very interesting and the authors should make more discussions about it. 5. The obtained cellulose trimellitate showed relatively good solubility in aqueous solution ( Figure 3). Then, if its solids show water/heating-responsive RTP effect for the destructive effect of water to the intermolecular interactions? 6. Some important references related to this work should be added, such as Sci. Adv. 2022, 8, eabl8392;Chem. Soc. Rev., 2021, 50, 12616;Chinese J. Chem., 2022, 40, 2359Acc. Chem. Res., 2020, 53, 962 and so on.
Reviewer #4 (Remarks to the Author): In this manuscript entitled "Aggregation-Regulated Room-Temperature Phosphorescence Materials with Multi-Mode Emission, Adjustable Excitation-Dependence and Visible-Light Excitation", You et al. presented RTP materials with multiple emission and special excitation modes by controlling the aggregation state of CBtCOONa. The strategy is simple, novel, and interesting. It provided a new strategy to fabricate RTP materials. The manuscript is well written and describes very thoroughly the synthesis processes and the applications of the RTP materials. It has a wide readership. It is suitable to the scope of NATURE COMMUNICATIONS. I recommend publishing this paper after minor revisions. 1. Are the RTP materials crystal or amorphous? XRD spectra of the RTP materials should be shown. 2. Except the reported metal ions, what is the effect of other common metal ions, such as Fe2+, Fe3+, Cu2+, Co2+ and so on? 3. Cellulose could demonstrate as a chiral polymer. Is the RTP chiral? Answer: Thanks for your kind comments. We have revised the manuscript as suggestion.

Answers to Comments by
(2) Reviewer #1 wrote: The authors mentioned that the degree of substitution (DS) of CBtCOOH was 0.54. However, the synthetic method indicated that they used different molars of trimellitic anhydride (9.48-14.22 g, 49.38-74.07 mmol). Hence, did the author optimize the reaction to obtain the DS? Whether the products with different molar ratios of trimellitic anhydride could show different RTP performance?
Answer: Thanks for your kind suggestion. We have synthesized a series of CBtCOOH with different DS values from 0.33 to 1.12 by controlling the reaction time and the molar ratio of trimellitic anhydride (BtCOOH) and AGU (Table R1).
The quantum yield of CBtCOONa (DS = 0.54) is 3.14% and the RTP lifetime is 240 ms, which is higher than those of other samples ( Figure R1). Therefore, we used CBtCOONa with DS = 0.54 as the raw materials. The synthesis results have added in the revised Supplementary Information. Answer: When the sodium trimellitate (BtCOONa) was chose as the raw materials and the same preparation method was used, we obtained only two types of RTP materials, which are green RTP material with a weak excitation-dependence and green/blue RTP material with a strong excitation-dependence ( Figure R2a). The RTP material with only blue phosphorescence was unable to be prepared. Because the molecularly dispersed state of trimellitate group is difficultly obtained, if there is not a polymer chain to immobilize the trimellitate group. In addition, the RTP lifetime and quantum yield of CBtCOONa were higher than those of BtCOONa      (5) Reviewer #1 wrote: For Fig. 2, the QYs for all these samples are smaller than 4%, which is a much lower value than other reported RTP systems. The authors may add some comments to it.
Answer: Thanks for your kind suggestion. The quantum yield of BtCOONa is only 2.91%. After being immobilized on cellulose chains, the quantum yield of obtained CBtCOONa (DS = 0.54) increases to 3.41% ( Figure R3a). The ISC effect can be promoted via the heavy-atom effect, molecular aggregation, lone-pair electron incorporation, energy-gap narrowing, and so on (Nat. Chem. 2011, 3, 205-210;Chem. Sci. 2017, 8, 590-599;Adv. Opt. Mater. 2019, 7, 1800820). We will introduce heavy-atom to promote the quantum yield in our further work. Answer: Thanks for your kind suggestion. The hydrodynamic radius (Rh) of single polymer chain is in a range of 10-50 nm, which depends on the molecular weight of polymer. As the concentration increases, polymer chains form the aggregate, the Rh of which is larger than 50 nm. The similar phenomena have been reported. For example, the Rh of cellulose in dilute solution is around 20 nm ( Figure R7) (Green Chem., 2022, 24, 3824-3833;Polymer, 2001, 42, 6765-6773;Green Chem., 2022, 24, 3824-3833;Carbohydr. Polym. 2014, 112, 125-133;Phys. Chem. Chem. Phys, 2022, 00, 1-3). As the concentration increases, the cellulose chains form the aggregate, the Rh of which is near or greater than 100 nm.  Under a strong stirring, the CBtCOONa/CaCO3 aqueous suspension was obtained.
The detailed method was shown in the manuscript.
(10) Reviewer #1 wrote: For Fig. 5a, this diagram is oversimplified and doesn't show how to fabricate patterns with those inks. Besides, the detailed methods to fabricate these patterns should be described in the Method.
Answer: Thanks for your kind suggestion. We have revised the diagram about how to fabricate patterns in our manuscript. Moreover, the detailed methods are added in the Method. In addition, the design for the complex RTP pattern was shown in Figure R8, and was added in the Supplementary Information.

Figure R8
Design schematic for a complex RTP pattern.
(11) Reviewer #1 wrote: For Fig. 4  Answer: Thanks for your nice comments and recommendation.
(2) Reviewer #2 wrote: The synthesis of CBtCOOH is proved by 1 H NMR and FTIR in the manuscript. However, these characterizations can only verify the coexistence of the cellulose chain and the small molecule in the system, while whether these two parts are conjugated is not sufficiently proved.
Answer: Thanks for your kind suggestion. We mixed the cellulose and sodium trimellitate (BtCOONa) to detect the FTIR. In the mixture of cellulose and BtCOONa, there is a peak at 1590 cm -1 ( Figure R9), which belongs to the C=O peak of COONa. In the FTIR spectrum of CBtCOONa, there is a new peak 1712 cm -1 which is the C=O peak of the ester group. Thus, the BtCOONa was immobilized on cellulose chain by the ester bond.
In addition, the cellulose/BtCOONa mixture exhibited weaker phosphorescence performance than CBtCOONa, as shown in Figure R10. (3) Reviewer #2 wrote: Line163-164, it is claimed that there is no excitation dependence at 254-310 nm excitation when CBtCOONa content is 4%-20%, which seems not accurate. The main peak is slightly red-shifted as the excitation wavelength changes from 254 to 310 nm in Figure S4(a).
Answer: Thanks for your kind suggestion. We have corrected the description in the manuscript.
Answer: Thanks for your kind suggestion. We have revised in the manuscript.

Are there any further evidences for it?
Answer: Thanks for your kind suggestion. The RTP lifetime and quantum yield of CBtCOONa are better than those of BtCOONa ( Figure R11 and R12), indicating that the ISC process has been promoted after bonding BtCOONa onto cellulose chain.  Answer: Thanks for your nice suggestion. We have cited some relative articles to explain this deduction in the manuscript (Angew. Chem. Int. Ed. 2018, 57, 678-682;Nat. Commun. 2019, 10, 4247;Sci. China. Chem. 2022, 66, 367-387 phosphorescence performance than CBtCOONa, as shown in Figure R13. The RTP intensity of the cellulose/BtCOONa mixture is much weaker than that of CBtCOONa with 365 nm lamp off. Moreover, the cellulose/BtCOONa mixture dose not exhibit RTP property after the visible light is turned off. These above phenomena illustrated the importance of the covalent linkage between anionic phenylcarboxylate and cellulose.    Photographs of CBtCOONa film. (5) Reviewer #3 wrote: In Figure 1 and 4, the afterglow times of aggregates are always longer than those of single molecular chains. This is very interesting and the authors should make more discussions about it.
Answer: Thanks for your kind suggestion. The more efficient ISC observed in aggregates is ascribed to possible ISC channels formed thanks to energy-level splitting. When moving from monomer to aggregate, substantial electronic interactions among chromophores cause overlap between the excitonic orbitals and, thus, give rise to energy splitting ( Figure R15). The splitting can generate more ISC channels and potentially boost ISC and RTP efficiency in aggregates (Nat. Rev. Mater. 2020, 5, 869-885).
(6) Reviewer #3 wrote: The obtained cellulose trimellitate showed relatively good solubility in aqueous solution (Figure 3) When water was removed, the intermolecular hydrogen bonds were constructed again. CBtCOONa exhibited RTP emission again ( Figure R16). Figure R16. Photographs of the reversible heating/water responsiveness process of CBtCOONa.
Answer: Thanks for your kind suggestion. We have cited the highly-related work in the revised manuscript.

Answers to Comments by Reviewer # 4
(1) Reviewer #4 wrote: In this manuscript entitled "Aggregation-Regulated Room- Answer: Thanks for your nice comments and recommendation.
(2) Reviewer #4 wrote: Are the RTP materials crystal or amorphous? XRD spectra of the RTP materials should be shown.
Answer: Thanks for your kind suggestion. XRD spectra of CBtCOOM show that the RTP materials are amorphous ( Figure R17a). XRD spectrum of CBtCOONa/CaCO3 indicates the RTP material has CaCO3 crystal ( Figure R17b). Answer: Thanks for your kind suggestion. As shown in Figure R18, the phosphorescence cannot be detected, when the Fe 2+ , Fe 3+ , Cu 2+ , Cu + , Co 2+ and Cr 3+ ions were used.

Figure R18
Photographs and phosphorescence spectra of CBtCOOM with some common metal ions.
(4) Reviewer #4 wrote: Cellulose could demonstrate as a chiral polymer. Is the RTP chiral?
Answer: Thanks for your kind suggestion. We have measured circularly polarized luminescence of CBtCOONa. As shown in Figure R19, there are a strong chiral fluorescence peak at 420 nm and a weak chiral phosphorescence peak at 510 nm, which demonstrate that the CBtCOONa emits chiral RTP.